The maximum temperature of many devices is exactly defined. Free air circulation is often insufficient and, in such cases, forced cooling is necessary to cool electric devices in a frequency converter.
Earlier, frequency converters have been cooled by fans that transfer cooling replacement air from outside the casing. For instance, publications U.S. Pat. No. 6,091,604; U.S. Pat. No. 5,617,307; and DE 10,103,941 disclose an encased frequency converter that is cooled using airflow produced by a fan.
To ensure sufficient cooling and firmness, complex structures are, however, required, whereby the size of the device increases and serviceability becomes difficult due to a layered structure, as disclosed in U.S. Pat. No. 6,091,604, for instance.
Liquid cooling has been applied to some extent to the cooling of electric devices by using ionized water, for instance. It has then been possible to bring the liquid in contact with electric circuits. When using another liquid, such as ordinary water, the liquid circulation needs to be kept separate from electric circuits, and this has caused problems in positioning the elements.